1. Field of the Invention
The present invention relates to a controller of an internal combustion engine for calculating rotation speed of the engine and for improving startability of the engine.
2. Description of Related Art
A control system of an internal combustion engine calculates engine rotation speed in a predetermined cycle to comprehend an engine operation state. For example, a control system described in Japanese Patent No. 3490541 calculates a time difference between pulses outputted from a sensor every time a crankshaft of the engine rotates through a predetermined crank angle (CA) and calculates the engine rotation speed based on summation calculation value of a predetermined number of the time differences corresponding to one engine stroke (180° CA). Thus, the control system calculates the engine rotation speed averaging an influence of condensation and rarefaction of a generation frequency of the pulse signals (fluctuation of a pulse signal generation cycle) during one stroke.
In recent years, accurate control of a combustion state or generated torque of the engine has been required in order to improve fuel consumption, exhaust emission, drivability of the engine and the like. Therefore, it is necessary to accurately comprehend the actual combustion state or generated torque.
Generally, the generated torque changes in accordance with the combustion state of the engine, and the engine rotation speed changes. Therefore, the engine rotation speed is information to evaluate the combustion state or the generated torque. However, since the control system of Japanese Patent No. 3490541 calculates the engine rotation speed averaging the influence of the condensation and rarefaction of the generation frequency of the pulse signals during one stroke (engine rotation fluctuation due to the change in the combustion state or the generated torque), correlation between the engine rotation speed and the combustion state or the generated torque is reduced. If the engine rotation speed having the reduced correlation with the combustion state or the generated torque of the engine is used as the information of the combustion state or the generated torque when the combustion state or the generated torque is controlled, the combustion state or the generated torque cannot be controlled accurately.
During a start-up of the internal combustion engine or before completion of a warm-up of the engine after the start-up, there is a possibility that a paddled fuel amount (wet amount) to a wall surface of an air-intake port varies due to a variation in a property (volatility) of used fuel and an air-fuel ratio of a mixture gas (combustion air-fuel ratio) in a cylinder deviates from a target air-fuel ratio. This can deteriorate startability or exhaust emission. As a countermeasure, a control system described in JP-A-H08-284708 senses a rotation fluctuation for each combustion stroke immediately after the start-up of the engine and learns a combustion property based on summation data obtained by summing the rotation fluctuations by predetermined times. The control system corrects a fuel injection amount based on the learning value of the combustion property.
A control system described in Japanese patent No. 3498392 performs correction for increasing the fuel injection amount when the control system senses a start-up of the engine that is not optimum based on a time necessary for the rotation speed to exceed a predetermined rotation speed after the start-up, the initial maximum rotation speed immediately after the start-up, a rotation speed change rate since the rotation speed exceeds the predetermined rotation speed until the rotation speed reaches the maximum rotation speed immediately after the start-up, the minimum rotation speed after the maximum rotation speed and the like.
However, the control system of JP-A-H08-284708 cannot perform appropriate fuel correction corresponding to the fuel property before the learning of the fuel property sufficiently advances after the start-up of the engine. Accordingly, there is a possibility that a deviation in the air-fuel ratio is generated due to the fuel property and the rotation speed fluctuation is caused.
The control system described in Japanese Patent No. 3498392 performs the correction for increasing the fuel injection amount after the start-up of the engine that is not optimum is sensed. Therefore, there is a possibility that the rotation speed fluctuation is caused before the start-up that is not optimum is sensed.
Moreover, as shown in FIG. 6, if the air-fuel ratio λ deviates from the target air-fuel ratio λt toward a lean side during the start-up of the engine due to a fuel property of the used fuel, a temporal change of the engine or the like, the generated torque correspondingly decreases from the torque Tt that should be obtained at the target air-fuel ratio λt. In FIG. 6, C represents a range in which the combustion torque does not increase even if the fuel is increased, D is a range in which the combustion torque increases if the fuel amount is increased, Qc is a fuel increase necessary for correcting the torque, and Tf is a decrease of the torque, for example, due to heavy fuel. The above-described control systems do not consider the torque fluctuation during the start-up. Therefore, even if the generated torque is deviated from the appropriate torque corresponding to the target air-fuel ratio, the deviation of the torque cannot be corrected. As a result, the engine cannot be started smoothly with an appropriate rotation speed behavior.